Pretty much the amount of options. It gives you just about any option you can want to tweak, like I mentioned earlier with the transmitting power (helps boost wireless signal), quality of service, wireless distribution system, RADIUS, overclocking abilities, etc.
Really, if you have a router that can be changed over to DD-WRT, you should do it. It only improves on what you're already using and doesn't make anything any harder. Here is a good guide on some tweaks for it if you're interested:
http://lifehacker.com/software/route...ter-178132.php